A ridge of energy on the surface of the water, caused by a disturbance, which then progresses from one point to another. Wind waves are generated by friction between the wind and the water that transfers energy to the water in the form of waves. As the waves grow larger with continued wind, the energy will also transfer deeper below the ocean surface. As the waves move out of the storm area, the stronger waves with more energy below the ocean surface (longer period waves with greater wavelengths) will maintain their strength over distance and will be characterised as deep water waves or swell. Smaller, shorter period waves generally limited to the ocean surface will tend to decay more rapidly after leaving the wave generating area. As the waves eventually arrive along the coast they will shoal over shallower water and break, becoming surf.